In this fourth and final article in a four-part series, I will look at how manufacturing electronic printed circuit board (PCB) board assemblies has evolved since the mid-1980s.
Part I: Electronics Manufacturing Review
Part II: Schematics – Then and Now
Part III: PCB Design – Then and Now
Part IV: Electronics Assembly – Then and Now
Circuit designers and PCB designers create electronic assemblies on paper, but to be of any use at all, the paper designs need to be transformed into an actual product. This is where the electronics manufacturing facilities provide their services.
A typical PCB assembly manufacturing process includes:
- Gathering all the documentation – schematic, PCB files, bill of materials (BoM)
- Purchasing the components called out in the BoM
- Installing the components onto the PCB
- Inspect that the work was done as prescribed
- Optionally test the final electronics product
Manufacturing in the 1980s
When I started my engineering career in 1984, automation and computers did not exist. An electronics manufacturing floor layout typically consisted of a lot of solder specialists working on benches (sometimes even static control benches) and bins of components. If there were 10 different resistors, 10 different capacitors, and 10 different transistors, diodes or integrated circuits, there would be 30 bins, one for each type of component. All of them were through hole. The circuits I used had ½ watt and 2 watt 5% resistors, which were color coded. High dollar 2% resistors were also available.
The “automation” was to assign each solder specialist to a handful of components. The repetitiveness of soldering the same components repeatedly helped to reduce human error. The board would then go to the next person and so on until it was complete.
The boards would then go to an inspector, who would do his or her best to make sure all the components were present and read the color codes on the resistors to make sure none got placed on the wrong locations. Rarely was a board built correctly and any defects found would be sent back to rework. The human error part of assembling boards was a significant problem.
Once through inspection, the products would be tested. Some of the products I worked on were for RADAR systems and had voltages more than 20kV. While I thought the solder specialists and inspectors were good, the risk of turning the board on without some pre-check was too high, so the testing of each product took significant time.
If I remember correctly, from start to finish, to build one working board was about a weeklong process.
Early Surface Mount Technology (SMT) Arrives
When surface mount devices (SMD) entered the electronics manufacturing industry, they were cautiously introduced into the design, although sparingly. They were the larger SMD components – probably 0805 was the smallest. This also brought another challenge – what was the best way to install them? They were very small, so a microscope became a must-have. Using two soldering irons to install them also became a necessity.
One of my co-workers worked with some of the earliest surface mount technology (SMT) machines (also known as pick and place machines). With them, you would grab a part, carefully place it where it needs to go (like a claw machine), then hit a button for the SMT machine to learn that location. Repeat for the other components, and voila, you had a SMT program. Thankfully, technology quickly advanced past that point.
Ball grid arrays (BGAs) then made a splash. BGAs have all the electrical connections under the component. When we first saw them, we had no idea how to install them since we could not get a soldering iron under the part. The answer was a heat gun. You also needed an X-ray machine to inspect them if you could afford one.
Modern PCB Assembly
High-volume manufacturing is possible today because of the advancements in technology and automation. The schematic tools feed into the PCB layout tools, which then feed into the whole assembly process.
Solder Stencils
Using the CAD data from the PCB Gerbers (files that define how a PCB is fabricated), a thin piece of metal is milled to expose the component pads that should have solder applied. At that point, solder paste is spread over the stencil which will be the solder used to connect all the components.
Pick and Place
The components are loaded into magazines that then go into the pick and place machine. The BoM and the CAD data are used to precisely place all these components. There is also a feature called electronic verification and test (EVT) that will measure all passive components, such as resistors and capacitors and stop if they are not the correct value.
Reflow
Once all the required parts are placed on the board, the board and its components are placed on a conveyor which takes it through a journey of heat zones. The solder melts, allowing the electrical components to connect where they should, then resolidifies locking them in place there.
Inspection
The CAD data is loaded into the automated optical inspection (AOI) machine which will look at all solder connections and component markings to make sure everything is correct. Components with leads not visible are X-rayed.
Through Hole Soldering
Several options are available – hand solder, wave solder (which has a fountain of solder that flows and usually requires a wave pallet to protect other components), or selective solder which again uses CAD data to know where to solder.
These advances in manufacturing technology allows for high-volume production and much better first-time pass rates than ever before. Looking back, the progression seems obvious, but starting back in the 1980s, I had no idea how fast the electronics manufacturing industry would evolve. When I think back to how it was and what it is now, I am still amazed. I wonder what will be in our future that none of us can imagine yet. Although I am certain robotics are in our very near future, probably sprinkled with some artificial intelligence.
If you would like to be part of this fascinating and fast-paced industry, keep an eye on our careers page. We have facilities in Maryland, North Carolina and Connecticut.
Bob DiDonato
Engineering Program Manager